1. Field of the Invention
This invention relates generally the production of lead flashing items, and more particularly to an apparatus using a welding process to produce said items.
2. Description of the Prior Art
Flashing is commonly used on roofs at locations where a pipe or the like passes through the roof. The purpose is to prevent rain water from running down the outside of the pipe and leaking into the building. Lead flashing is particularly useful because it is extremely pliable and can therefore be easily bent to fit over the top of the pipe and to conform to the roof line.
Building codes generally specify a minimum thickness of the lead to be used in flashing. For example, flashing meeting a specification requiring flashing weighing two and one-half pounds per square foot is produced using lead sheets 0.039 inches thick. Both the cylinder portion and the flat sheet portion of the pipe flashing are therefore made from lead having the same thickness.
Lead flashing for a pipe is formed from a flat sheet with a circular hole punched from it which is joined to a cylinder. The cylinder may be formed by extrusion or by bending a flat sheet around a cylindrical form and making a butt joint of some type. It is common practice to make a butt joint between two lead edges by application of heat at the joint, with or without the addition of supplementary lead or solder, so that forming a lead cylinder is not particularly difficult. If however, the ends are overlapped and heat is applied by torch, the top layer of lead will melt and run off before the bottom layer becomes hot enough to fuse the two layers together.
The joint between the flat sheet and the cylinder is conventionally formed by placing the flat sheet (with the cylinder standing on it in the desired location) on a horizontally oriented, rotating table. The operator uses a torch to melt a bar of lead or solder so that it will form a bead of supplementary lead or solder completely around the cylinder at its juncture with the flat sheet. The operator controls the rate of rotation of the table by letting it rub against his hand and also holds the torch and the bar of lead or solder in the proper position. If the speed of rotation is too slow or the torch is held too close, a hole will result and the product may be ruined beyond repair. If the operator tries to avoid holes by permitting the table to rotate too fast or keeping the torch too far from the juncture, fusion between the supplementary metal and the lead sheet and cylinder being joined will not occur.
Some fabrication errors can be corrected after they are discovered, but spoilage and excessive time of fabrication have made production of lead flashing for pipes costly, particularly with unskilled workers. An unskilled worker typically may produce 60 usable flashing products in one eight hour day using this existing technique. Approximately three months of experience are needed before an acceptable level of 500 products per day is achieved.
The low production rate and high spoilage (especially with unskilled workers) make production by the conventional method expensive because of labor costs; and the cost of the additional lead or solder used to make the bead is an added detrimental factor. There are other methods which are currently used such as using a ring of solder which is postioned at the joint and then melted, and forming the bead on the bottom of the flat sheet, but these have the same objectionable features.
It is therefore an object of this invention to provide a method of producing lead flashing which is less dependent upon skill than conventional methods.
It is also an object of this invention to provide a method of producing lead flashing which results in less spoilage.
It is an additional object of this invention to produce lead flashing without the need for adding additional metal to form the joint.